Improved Nb SIS devices for heterodyne mixers between 700 GHz and 1.3 THz with NbTiN transmission lines using a normal metal energy relaxation layer

TL;DR

This paper presents an improved Nb SIS device with a normal metal layer to enhance heterodyne mixer performance in the 700 GHz to 1.3 THz range, demonstrating reduced quasiparticle heating and potential for better THz signal mixing.

Contribution

Introduction of a niobium-trilayer junction with a gold normal metal layer to mitigate quasiparticle heating in high-frequency heterodyne mixers.

Findings

Normal metal layer reduces quasiparticle heating.

Device geometry affects quasiparticle cooling efficiency.

Potential for improved THz heterodyne mixer performance.

Abstract

In this paper we demonstrate experimentally the implementation of a niobium-trilayer junction with an aluminum-oxide tunnel barrier, embedded in a high-gap superconducting niobium-titanium-nitride circuit. Previously reported heating by quasiparticle trapping is removed by inserting a normal metal layer of gold between the niobium junction and the niobium-titanium-nitride layer. We analyze in dc-characterization measurements the cooling of the nonequilibrium quasiparticles in various device geometries having different gold layer thickness and shape. Our work is concluded with remarks for future heterodyne mixer experiments using our device technology.